Method and apparatus for transmitting relay support indication in wireless communication system

ABSTRACT

A method and apparatus for performing a cell selection or a cell reselection in a wireless communication system is provided. A user equipment (UE) receives information on whether a cell supports a relay functionality or not, and performs a cell selection or a cell reselection according to the information. If the information indicates that the cell does not support the relay functionality, the cell can be considered as barred for relay functionality.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Phase of PCT/KR2016/003571 filed onApr. 6, 2016, which claims priority under 35 U.S.C. § 119(e) to U.S.Provisional Application No. 62/144,347 filed on Apr. 8, 2015, all ofwhich are hereby expressly incorporated by reference into the presentapplication.

TECHNICAL FIELD

The present invention relates to wireless communications, and moreparticularly, to a method and apparatus for transmitting a relay supportindication in a wireless communication system.

BACKGROUND ART

3rd generation partnership project (3GPP) long-term evolution (LTE) is atechnology for enabling high-speed packet communications. Many schemeshave been proposed for the LTE objective including those that aim toreduce user and provider costs, improve service quality, and expand andimprove coverage and system capacity. The 3GPP LTE requires reduced costper bit, increased service availability, flexible use of a frequencyband, a simple structure, an open interface, and adequate powerconsumption of a terminal as an upper-level requirement.

Recently, there has been a surge of interest in supportingproximity-based services (ProSe). Proximity is determined (“a userequipment (UE) is in proximity of another UE”) when given proximitycriteria are fulfilled. This new interest is motivated by severalfactors driven largely by social networking applications, and thecrushing data demands on cellular spectrum, much of which is localizedtraffic, and the underutilization of uplink frequency bands. 3GPP istargeting the availability of ProSe in LTE rel-12 to enable LTE become acompetitive broadband communication technology for public safetynetworks, used by first responders. Due to the legacy issues and budgetconstraints, current public safety networks are still mainly based onobsolete 2G technologies while commercial networks are rapidly migratingto LTE. This evolution gap and the desire for enhanced services have ledto global attempts to upgrade existing public safety networks. Comparedto commercial networks, public safety networks have much more stringentservice requirements (e.g., reliability and security) and also requiredirect communication, especially when cellular coverage fails or is notavailable. This essential direct mode feature is currently missing inLTE.

By using concept of ProSe function, the extension of network coverageusing L3-based UE-to-Network Relay and/or UE-to-UE Relay have beendiscussed. For UE-to-Network Relay, there may be a network that supportsrelay functionality and does not support relay functionality.Accordingly, it is desirable that the UE is camped on a cell whichsupports relay functionality.

Disclosure Of Invention Technical Problem

The present invention provides a method and apparatus for transmitting arelay support indication in a wireless communication system. The presentinvention provides a method and apparatus for transmitting informationon whether a cell supports relay functionality or not.

Solution to Problem

In an aspect, a method for performing, by a user equipment (UE), a cellselection or a cell reselection in a wireless communication system isprovided. The method includes receiving information on whether a cellsupports a relay functionality or not, and performing a cell selectionor a cell reselection according to the information.

In another aspect, a user equipment (UE) in a wireless communicationsystem is provided. The UE includes a memory, a transceiver, and aprocessor coupled to the memory and the transceiver. The processor isconfigured to control the transceiver to receive information on whethera cell supports a relay functionality or not, and perform a cellselection or a cell reselection according to the information.

Advantageous Effects of Invention

UE-to-Network Relay can be performed efficiently.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows LTE system architecture.

FIG. 2 shows a block diagram of architecture of a typical E-UTRAN and atypical EPC.

FIG. 3 shows a block diagram of a user plane protocol stack of an LTEsystem.

FIG. 4 shows a block diagram of a control plane protocol stack of an LTEsystem.

FIG. 5 shows an example of a physical channel structure.

FIG. 6 shows a user plane protocol stack for ProSe direct communication.

FIG. 7 shows a control plane protocol stack for ProSe directcommunication.

FIG. 8 shows PC5 interface for ProSe direct discovery.

FIG. 9 shows an example of UE-to-Network Relay and UE-to-UE Relay.

FIG. 10 shows a method for transmitting a relay support indicationaccording to an embodiment of the present invention.

FIG. 11 shows a wireless communication system to implement an embodimentof the present invention.

MODE FOR THE INVENTION

The technology described below can be used in various wirelesscommunication systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc. The CDMA canbe implemented with a radio technology such as universal terrestrialradio access (UTRA) or CDMA-2000. The TDMA can be implemented with aradio technology such as global system for mobile communications(GSM)/general packet ratio service (GPRS)/enhanced data rate for GSMevolution (EDGE). The OFDMA can be implemented with a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), etc.IEEE 802.16m is an evolution of IEEE 802.16e, and provides backwardcompatibility with an IEEE 802.16-based system. The UTRA is a part of auniversal mobile telecommunication system (UMTS). 3rd generationpartnership project (3GPP) long term evolution (LTE) is a part of anevolved UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE uses the OFDMA indownlink and uses the SC-FDMA in uplink LTE-advance (LTE-A) is anevolution of the 3GPP LTE.

For clarity, the following description will focus on the LTE-A. However,technical features of the present invention are not limited thereto.

FIG. 1 shows LTE system architecture. The communication network iswidely deployed to provide a variety of communication services such asvoice over internet protocol (VoIP) through IMS and packet data.

Referring to FIG. 1, the LTE system architecture includes one or moreuser equipment (UE; 10), an evolved-UMTS terrestrial radio accessnetwork (E-UTRAN) and an evolved packet core (EPC). The UE 10 refers toa communication equipment carried by a user. The UE 10 may be fixed ormobile, and may be referred to as another terminology, such as a mobilestation (MS), a user terminal (UT), a subscriber station (SS), awireless device, etc.

The E-UTRAN includes one or more evolved node-B (eNB) 20, and aplurality of UEs may be located in one cell. The eNB 20 provides an endpoint of a control plane and a user plane to the UE 10. The eNB 20 isgenerally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as a base station (BS), anaccess point, etc. One eNB 20 may be deployed per cell.

Hereinafter, a downlink (DL) denotes communication from the eNB 20 tothe UE 10, and an uplink (UL) denotes communication from the UE 10 tothe eNB 20. In the DL, a transmitter may be a part of the eNB 20, and areceiver may be a part of the UE 10. In the UL, the transmitter may be apart of the UE 10, and the receiver may be a part of the eNB 20.

The EPC includes a mobility management entity (MME) and a systemarchitecture evolution (SAE) gateway (S-GW). The MME/S-GW 30 may bepositioned at the end of the network and connected to an externalnetwork. For clarity, MME/S-GW 30 will be referred to herein simply as a“gateway,” but it is understood that this entity includes both the MMEand S-GW.

The MME provides various functions including non-access stratum (NAS)signaling to eNBs 20, NAS signaling security, access stratum (AS)security control, inter core network (CN) node signaling for mobilitybetween 3GPP access networks, idle mode UE reachability (includingcontrol and execution of paging retransmission), tracking area listmanagement (for UE in idle and active mode), packet data network (PDN)gateway (P-GW) and S-GW selection, MME selection for handovers with MMEchange, serving GPRS support node (SGSN) selection for handovers to 2Gor 3G 3GPP access networks, roaming, authentication, bearer managementfunctions including dedicated bearer establishment, support for publicwarning system (PWS) (which includes earthquake and tsunami warningsystem (ETWS) and commercial mobile alert system (CMAS)) messagetransmission. The S-GW host provides assorted functions includingper-user based packet filtering (by e.g., deep packet inspection),lawful interception, UE Internet protocol (IP) address allocation,transport level packet marking in the DL, UL and DL service levelcharging, gating and rate enforcement, DL rate enforcement based onaccess point name aggregate maximum bit rate (APN-AMBR).

Interfaces for transmitting user traffic or control traffic may be used.The UE 10 is connected to the eNB 20 via a Uu interface. The eNBs 20 areconnected to each other via an X2 interface. Neighboring eNBs may have ameshed network structure that has the X2 interface. A plurality of nodesmay be connected between the eNB 20 and the gateway 30 via an S1interface.

FIG. 2 shows a block diagram of architecture of a typical E-UTRAN and atypical EPC. Referring to FIG. 2, the eNB 20 may perform functions ofselection for gateway 30, routing toward the gateway 30 during a radioresource control (RRC) activation, scheduling and transmitting of pagingmessages, scheduling and transmitting of broadcast channel (BCH)information, dynamic allocation of resources to the UEs 10 in both ULand DL, configuration and provisioning of eNB measurements, radio bearercontrol, radio admission control (RAC), and connection mobility controlin LTE_ACTIVE state. In the EPC, and as noted above, gateway 30 mayperform functions of paging origination, LTE_IDLE state management,ciphering of the user plane, SAE bearer control, and ciphering andintegrity protection of NAS signaling.

FIG. 3 shows a block diagram of a user plane protocol stack of an LTEsystem. FIG. 4 shows a block diagram of a control plane protocol stackof an LTE system. Layers of a radio interface protocol between the UEand the E-UTRAN may be classified into a first layer (L1), a secondlayer (L2), and a third layer (L3) based on the lower three layers ofthe open system interconnection (OSI) model that is well-known in thecommunication system.

A physical (PHY) layer belongs to the L1. The PHY layer provides ahigher layer with an information transfer service through a physicalchannel. The PHY layer is connected to a medium access control (MAC)layer, which is a higher layer of the PHY layer, through a transportchannel. A physical channel is mapped to the transport channel. Databetween the MAC layer and the PHY layer is transferred through thetransport channel. Between different PHY layers, i.e. between a PHYlayer of a transmission side and a PHY layer of a reception side, datais transferred via the physical channel.

A MAC layer, a radio link control (RLC) layer, and a packet dataconvergence protocol (PDCP) layer belong to the L2. The MAC layerprovides services to the RLC layer, which is a higher layer of the MAClayer, via a logical channel. The MAC layer provides data transferservices on logical channels. The RLC layer supports the transmission ofdata with reliability. Meanwhile, a function of the RLC layer may beimplemented with a functional block inside the MAC layer. In this case,the RLC layer may not exist. The PDCP layer provides a function ofheader compression function that reduces unnecessary control informationsuch that data being transmitted by employing IP packets, such as IPv4or IPv6, can be efficiently transmitted over a radio interface that hasa relatively small bandwidth.

A radio resource control (RRC) layer belongs to the L3. The RLC layer islocated at the lowest portion of the L3, and is only defined in thecontrol plane. The RRC layer controls logical channels, transportchannels, and physical channels in relation to the configuration,reconfiguration, and release of radio bearers (RBs). The RB signifies aservice provided the L2 for data transmission between the UE andE-UTRAN.

Referring to FIG. 3, the RLC and MAC layers (terminated in the eNB onthe network side) may perform functions such as scheduling, automaticrepeat request (ARQ), and hybrid ARQ (HARM). The PDCP layer (terminatedin the eNB on the network side) may perform the user plane functionssuch as header compression, integrity protection, and ciphering.

Referring to FIG. 4, the RLC and MAC layers (terminated in the eNB onthe network side) may perform the same functions for the control plane.The RRC layer (terminated in the eNB on the network side) may performfunctions such as broadcasting, paging, RRC connection management, RBcontrol, mobility functions, and UE measurement reporting andcontrolling. The NAS control protocol (terminated in the MME of gatewayon the network side) may perform functions such as a SAE bearermanagement, authentication, LTE_IDLE mobility handling, pagingorigination in LTE_IDLE, and security control for the signaling betweenthe gateway and UE.

FIG. 5 shows an example of a physical channel structure. A physicalchannel transfers signaling and data between PHY layer of the UE and eNBwith a radio resource. A physical channel consists of a plurality ofsubframes in time domain and a plurality of subcarriers in frequencydomain. One subframe, which is 1 ms, consists of a plurality of symbolsin the time domain. Specific symbol(s) of the subframe, such as thefirst symbol of the subframe, may be used for a physical downlinkcontrol channel (PDCCH). The PDCCH carries dynamic allocated resources,such as a physical resource block (PRB) and modulation and coding scheme(MCS).

A DL transport channel includes a broadcast channel (BCH) used fortransmitting system information, a paging channel (PCH) used for paginga UE, a downlink shared channel (DL-SCH) used for transmitting usertraffic or control signals, a multicast channel (MCH) used for multicastor broadcast service transmission. The DL-SCH supports HARQ, dynamiclink adaptation by varying the modulation, coding and transmit power,and both dynamic and semi-static resource allocation. The DL-SCH alsomay enable broadcast in the entire cell and the use of beamforming.

A UL transport channel includes a random access channel (RACH) normallyused for initial access to a cell, a uplink shared channel (UL-SCH) fortransmitting user traffic or control signals, etc. The UL-SCH supportsHARQ and dynamic link adaptation by varying the transmit power andpotentially modulation and coding. The UL-SCH also may enable the use ofbeamforming.

The logical channels are classified into control channels fortransferring control plane information and traffic channels fortransferring user plane information, according to a type of transmittedinformation. That is, a set of logical channel types is defined fordifferent data transfer services offered by the MAC layer.

The control channels are used for transfer of control plane informationonly. The control channels provided by the MAC layer include a broadcastcontrol channel (BCCH), a paging control channel (PCCH), a commoncontrol channel (CCCH), a multicast control channel (MCCH) and adedicated control channel (DCCH). The BCCH is a downlink channel forbroadcasting system control information. The PCCH is a downlink channelthat transfers paging information and is used when the network does notknow the location cell of a UE. The CCCH is used by UEs having no RRCconnection with the network. The MCCH is a point-to-multipoint downlinkchannel used for transmitting multimedia broadcast multicast services(MBMS) control information from the network to a UE. The DCCH is apoint-to-point bi-directional channel used by UEs having an RRCconnection that transmits dedicated control information between a UE andthe network.

Traffic channels are used for the transfer of user plane informationonly. The traffic channels provided by the MAC layer include a dedicatedtraffic channel (DTCH) and a multicast traffic channel (MTCH). The DTCHis a point-to-point channel, dedicated to one UE for the transfer ofuser information and can exist in both uplink and downlink The MTCH is apoint-to-multipoint downlink channel for transmitting traffic data fromthe network to the UE.

Uplink connections between logical channels and transport channelsinclude the DCCH that can be mapped to the UL-SCH, the DTCH that can bemapped to the UL-SCH and the CCCH that can be mapped to the UL-SCH.Downlink connections between logical channels and transport channelsinclude the BCCH that can be mapped to the BCH or DL-SCH, the PCCH thatcan be mapped to the PCH, the DCCH that can be mapped to the DL-SCH, andthe DTCH that can be mapped to the DL-SCH, the MCCH that can be mappedto the MCH, and the MTCH that can be mapped to the MCH.

An RRC state indicates whether an RRC layer of the UE is logicallyconnected to an RRC layer of the E-UTRAN. The RRC state may be dividedinto two different states such as an RRC idle state (RRC_IDLE) and anRRC connected state (RRC_CONNECTED). In RRC_IDLE, the UE may receivebroadcasts of system information and paging information while the UEspecifies a discontinuous reception (DRX) configured by NAS, and the UEhas been allocated an identification (ID) which uniquely identifies theUE in a tracking area and may perform public land mobile network (PLMN)selection and cell re-selection. Also, in RRC_IDLE, no RRC context isstored in the eNB.

In RRC_CONNECTED, the UE has an E-UTRAN RRC connection and a context inthe E-UTRAN, such that transmitting and/or receiving data to/from theeNB becomes possible. Also, the UE can report channel qualityinformation and feedback information to the eNB. In RRC_CONNECTED, theE-UTRAN knows the cell to which the UE belongs. Therefore, the networkcan transmit and/or receive data to/from UE, the network can controlmobility (handover and inter-radio access technologies (RAT) cell changeorder to GSM EDGE radio access network (GERAN) with network assistedcell change (NACC)) of the UE, and the network can perform cellmeasurements for a neighboring cell.

In RRC_IDLE, the UE specifies the paging DRX cycle. Specifically, the UEmonitors a paging signal at a specific paging occasion of every UEspecific paging DRX cycle. The paging occasion is a time interval duringwhich a paging signal is transmitted. The UE has its own pagingoccasion. A paging message is transmitted over all cells belonging tothe same tracking area. If the UE moves from one tracking area (TA) toanother TA, the UE will send a tracking area update (TAU) message to thenetwork to update its location.

Proximity-based services (ProSe) are described. “ProSe” may be usedmixed with “D2D”. ProSe direct communication means a communicationbetween two or more UEs in proximity that are ProSe-enabled, by means ofuser plane transmission using E-UTRA technology via a path nottraversing any network node. ProSe-enabled UE means a UE that supportsProSe requirements and associated procedures. Unless explicitly statedotherwise, a ProSe-enabled UE refers both to a non-public safety UE anda public safety UE. ProSe-enabled public safety UE means a ProSe-enabledUE that also supports ProSe procedures and capabilities specific topublic safety. ProSe-enabled non-public safety UE means a UE thatsupports ProSe procedures and but not capabilities specific to publicsafety. ProSe direct discovery means a procedure employed by aProSe-enabled UE to discover other ProSe-enabled UEs in its vicinity byusing only the capabilities of the two UEs with 3GPP LTE rel-12technology. EPC-level ProSe discovery means a process by which the EPCdetermines the proximity of two ProSe-enabled UEs and informs them oftheir proximity. ProSe UE identity (ID) is a unique identity allocatedby evolved packet system (EPS) which identifies the ProSe enabled UE.ProSe application ID is an identity identifying application relatedinformation for the ProSe enabled UE.

Sidelink is UE to UE interface for ProSe direct communication and ProSedirect discovery. Sidelink comprises ProSe direct discovery and ProSedirect communication between UEs. Sidelink uses UL resources andphysical channel structure similar to UL transmissions. Sidelinktransmission uses the same basic transmission scheme as the ULtransmission scheme. However, sidelink is limited to single clustertransmissions for all the sidelink physical channels. Further, sidelinkuses a 1 symbol gap at the end of each sidelink sub-frame.

For mapping between sidelink transport channels and sidelink physicalchannels, a sidelink discovery channel (SL-DCH) may be mapped to aphysical sidelink discovery channel (PSDCH), which carries ProSe directdiscovery message from the UE. The SL-DCH is characterized by:

-   -   fixed size, pre-defined format periodic broadcast transmission;    -   support for both UE autonomous resource selection and scheduled        resource allocation by eNB;    -   collision risk due to support of UE autonomous resource        selection; no collision when UE is allocated dedicated resources        by the eNB.

Further, a sidelink shared channel (SL-SCH) may be mapped to a physicalsidelink shared channel (PSSCH), which carries data from a UE for ProSedirect communication. The SL-SCH is characterized by:

-   -   support for broadcast transmission;    -   support for both UE autonomous resource selection and scheduled        resource allocation by eNB;    -   collision risk due to support of UE autonomous resource        selection; no collision when UE is allocated dedicated resources        by the eNB;    -   support for HARQ combining, but no support for HARQ feedback;    -   support for dynamic link adaptation by varying the transmit        power, modulation and coding.

Further, a sidelink broadcast channel (SL-BCH) may be mapped to aphysical sidelink broadcast channel (PSBCH), which carries system andsynchronization related information transmitted from the UE. The SL-BCHis characterized by pre-defined transport format.

A physical sidelink control channel (PSCCH) carries control from a UEfor ProSe direct communication. The PSCCH is mapped to the sidelinkcontrol resources. The PSCCH indicates resource and other transmissionparameters used by a UE for PSSCH.

For mapping between sidelink logical channels and sidelink transportchannels for ProSe direct communication, a sidelink broadcast controlchannel (SBCCH) may be mapped to the SL-BCH. The SBCCH is a sidelinkchannel for broadcasting sidelink system information from one UE toother UE(s). This channel is used only by ProSe direct communicationcapable UEs. Further, a sidelink traffic channel (STCH) may be mapped tothe SL-SCH. The STCH is a point-to-multipoint channel, for transfer ofuser information from one UE to other UEs. This channel is used only byProSe direct communication capable UEs.

ProSe direct communication is a mode of communication whereby UEs cancommunicate with each other directly over the PC5 interface. Thiscommunication mode is supported when the UE is served by E-UTRAN andwhen the UE is outside of E-UTRA coverage. Only those UEs authorized tobe used for public safety operation can perform ProSe directcommunication.

In order to perform synchronization for out of coverage operation, UE(s)may act as a synchronization source by transmitting SBCCH and asynchronization signal. SBCCH carries the most essential systeminformation needed to receive other ProSe channels and signals. SBCCHalong with synchronization signal is transmitted with a fixedperiodicity of 40 ms. When the UE is in network coverage, the contentsof SBCCH are derived from the parameters signaled by the eNB. When theUE is out of coverage, if the UE selects another UE as a synchronizationreference, then the content of SBCCH is derived from the received SBCCH.Otherwise, UE uses pre-configured parameters. System information block(SIB) 18 provides the resource information for synchronization signaland SBCCH transmission. There are two pre-configured subframes every 40ms for out of coverage operation. UE receives synchronization signal andSBCCH in one subframe and transmit synchronization signal and SBCCH onanother subframe if UE becomes synchronization source.

UE performs Prose direct communication on subframes defined over theduration of sidelink control period. The sidelink control period is theperiod over which resources allocated in a cell for sidelink control andsidelink data transmissions occur. Within the sidelink control period,the UE sends a sidelink control followed by sidelink data. Sidelinkcontrol indicates a layer 1 ID and characteristics of the transmissions(e.g. MCS, location of the resource(s) over the duration of sidelinkcontrol period, timing alignment).

The UE performs transmission and reception of Uu and PC5 with thefollowing decreasing priority order:

-   -   Uu transmission/reception (highest priority)    -   PC5 ProSe direct communication transmission/reception    -   PC5 ProSe direct discovery transmission/reception (lowest        priority)

FIG. 6 shows a user plane protocol stack for ProSe direct communication.Referring to FIG. 6, PDCP, RLC and MAC sublayers (terminate at the otherUE) perform the functions listed for the user plane. The AS protocolstack in the PC5-U interface consists of PDCP, RLC, MAC and PHY.

There is no HARQ feedback for ProSe direct communication. RLCunacknowledged mode (UM) is used for ProSe direct communication. Areceiving UE needs to maintain at least one RLC UM entity pertransmitting peer UE. A receiving RLC UM entity used for ProSe directcommunication does not need to be configured prior to reception of thefirst RLC unacknowledged mode data (UMD) protocol data unit (PDU).Robust header compression (ROHC) unidirectional mode is used for headercompression in PDCP for ProSe direct communication.

A UE may establish multiple logical channels. Logical channel ID (LCID)included within the MAC subheader uniquely identifies a logical channelwithin the scope of one source Layer-2 ID and ProSe layer-2 group IDcombination. Parameters for logical channel prioritization are notconfigured.

FIG. 7 shows a control plane protocol stack for ProSe directcommunication. Referring to FIG. 7, PDCP, the AS protocol stack forSBCCH in the PC5-C interface consists of RRC, RLC, MAC and PHY. A UEdoes not establish and maintain a logical connection to receiving UEsprior to a ProSe direct communication.

For ProSe direct communication, the UE supporting ProSe directcommunication can operate in two modes for resource allocation, whichinclude Mode 1 (scheduled resource allocation) and Mode 2 (UE autonomousresource selection). In Mode 1, the UE needs to be RRC_CONNECTED inorder to transmit data. The UE requests transmission resources from theeNB. The eNB schedules transmission resources for transmission ofsidelink control and data. The UE sends a scheduling request (dedicatedscheduling request (D-SR) or random access) to the eNB followed by aProSe buffer status report (BSR). Based on the ProSe BSR, the eNB candetermine that the UE has data for a ProSe direct communicationtransmission and estimate the resources needed for transmission. The eNBcan schedule transmission resources for ProSe direct communication usingconfigured sidelink radio network temporary identifier (SL-RNTI). InMode 2, a UE on its own selects resources from resource pools andperforms transport format selection to transmit sidelink control anddata.

A UE in RRC_CONNECTED may send a ProSe UE Information indication to eNBwhen UE becomes interested in ProSe Direct Communication. In responseeNB may configure the UE with a SL-RNTI.

A UE is considered in-coverage for ProSe direct communication wheneverit detects a cell on a public safety ProSe carrier. If the UE is out ofcoverage for ProSe direction communication, it can only use Mode 2. Ifthe UE is in coverage for ProSe direct communication, it may use Mode 1or Mode 2 as per eNB configuration. If the UE is in coverage for ProSedirect communication, it shall use only Mode 1 unless one of theexceptional cases occurs. When an exceptional case occurs, the UE isallowed to use Mode 2 temporarily even though it was configured to useMode 1. Resource pool to be used during exceptional case may be providedby eNB.

A UE that is camped or connected on one carrier frequency but interestedin ProSe direct communication operation on another carrier frequency(i.e. public safety ProSe carrier) shall attempt to find cells on thepublic safety ProSe carrier. An RRC_IDLE UE camped on a cell in anothercarrier frequency, but in the coverage area of an E-UTRA cell on publicsafety ProSe carrier, may consider the public safety ProSe carrier to behighest priority, and reselects to the cell on the public safety ProSecarrier. UE may consider a frequency (non-public safety ProSe carrier)to be highest priority if it can perform ProSe direct communication onlywhile camping on the frequency.

An RRC_CONNECTED UE served by a cell in another carrier frequency maysend a ProSe UE Information indication to its serving cell when it wantsto perform ProSe direct communication. The indication contains theintended public safety ProSe carrier. The serving cell indicates withthe presence of SIB 18 whether the UE is allowed to send the ProSe UEInformation indication. The serving cell may configure an interfrequencyradio resource management (RRM) measurement on the public safety ProSecarrier. Once the UE enters coverage of a cell on the public safetyProSe carrier, based on measurement report, the eNB performsinter-frequency mobility to the public safety ProSe carrier. Ifinter-frequency mobility is not performed by the serving cell, or if itfails, the UE may still perform ProSe direct communication using Mode 2from the resource pools, if any, broadcasted by the detected E-UTRA cellon the public safety ProSe carrier.

If the UE does not detect an E-UTRA cell on the public safety ProSecarrier, the UE can use public safety ProSe carrier resourcespreconfigured in the universal integrated circuit card (UICC) or mobileequipment (ME) for out of coverage ProSe direct communication. If the UEdetects an E-UTRA cell on the public safety ProSe carrier, the UE stopsusing resources preconfigured in the UICC or ME. UE may use Mode 2 fromthe resource pools, if any, broadcasted by the detected E-UTRA cell onthe public safety ProSe carrier. For Rel-12, all ProSe communication(for a UE) is performed on a single preconfigured public safety ProSecarrier, which is valid in the operating region. Higher layers checkvalidity of the public safety ProSe carrier in the operating region.

The cell on the public safety ProSe carrier may provide a transmissionresource pool for Mode 2 in SIB 18. UEs that are authorized for Prosedirect communication may use these resources for ProSe directcommunication in RRC_IDLE in the cell in the same carrier (i.e. publicsafety ProSe carrier). UEs that are authorized for ProSe directcommunication may use these resources for ProSe direct communication inRRC_IDLE in the cell on the same carrier (i.e. public safety ProSecarrier). UEs that are authorized for ProSe direct communication may usethese resources for ProSe direct communication in RRC_IDLE orRRC_CONNECTED in a cell on another carrier.

Alternatively, the cell on the public safety ProSe carrier may indicatein SIB 18 that it supports ProSe direct communication but does notprovide transmission resources. UEs need to enter RRC_CONNECTED toperform ProSe direct communication transmission. In this case, the cellon the public safety ProSe carrier may provide, in broadcast signaling,an exceptional transmission resource pool for Mode 2, to be used by theUE in exceptional cases. A UE in RRC_CONNECTED that is authorized toperform ProSe direct communication transmission indicates to the servingeNB that it wants to perform ProSe direct communication transmissions.The eNB validates whether the UE is authorized for ProSe directcommunication transmission using the UE context received from MME. TheeNB may configure a UE by dedicated signaling with a transmissionresource pool for Mode 2. That may be used without constraints while theUE is RRC_CONNECTED. Alternatively, the eNB may configure a UE to usethe exceptional transmission resource pool for Mode 2 which the UE isallowed to use only in exceptional cases, and rely on scheduled resourceallocation otherwise.

The resource pools for sidelink control when the UE is out of coverageare preconfigured for reception and transmission. The resource pools forsidelink control when the UE is in coverage for ProSe directcommunication are configured as below. The resource pool used forreception is configured by the eNB via RRC, in broadcast signaling. Theresource pool used for transmission is configured by the eNB via RRC, indedicated or broadcast signaling, if Mode 2 is used. The resource poolused for transmission is configured by the eNB via RRC, in dedicatedsignaling, if Mode 1 is used. The eNB schedules the specific resource(s)for sidelink control transmission within the configured reception pool.In order to perform communication even when some UEs are in-coverage andsome UEs are out of coverage, all UEs (i.e. both in and out of coverage)should be configured with reception resource pools for sidelink controlwhich are the union of the resource pools used for transmission ofsidelink control in the serving cell and neighbor cells and transmissionof sidelink control for out of coverage.

The resource pools for data when the UE is out of coverage for ProSedirect communication are pre-configured for reception and transmission.The resource pools for data when the UE is in coverage for ProSe directcommunication are configured by the eNB via RRC, in dedicated orbroadcast signaling, if Mode 2 is used, for reception and transmission.There is no resource pool for transmission if Mode 1 is used.

ProSe direct discovery is defined as the procedure used by the UEsupporting ProSe direct discovery to discover other UE(s) in itsproximity, using E-UTRA direct radio signals via PC5. ProSe directdiscovery is supported only when the UE is served by E-UTRAN. Upperlayer handles authorization for announcement and monitoring of discoverymessage. Content of discovery message is transparent to AS and nodistinction in AS is made for ProSe direct discovery models and types ofProSe direct discovery. The ProSe protocol ensures that only validdiscovery messages are delivered to AS for announcement.

The UE can participate in announcing and monitoring of discovery messagein both RRC_IDLE and RRC_CONNECTED states as per eNB configuration. TheUE announces and monitors its discovery message subject to thehalf-duplex constraint. The UE that participates in announcing andmonitoring of discovery messages maintains the current coordinateduniversal time coordinated (UTC) time. The UE that participates inannouncing transmits the discovery message which is generated by theProSe protocol taking into account the UTC time upon transmission of thediscovery message. In the monitoring UE, the ProSe protocol provides themessage to be verified together with the UTC time upon reception of themessage to the ProSe function.

In order to perform synchronization, UE(s) participating in announcingof discovery messages may act as a synchronization source bytransmitting a synchronization signal based on the resource informationfor synchronization signals provided in SIB19.

There are three range classes. Upper layer authorization providesapplicable range class of the UE. Maximum allowed transmission power foreach range class is signaled in SIB 19. UE uses the applicable maximumallowed transmission power corresponding to its authorized range class.This puts an upper limit on the determined transmit power based on openloop power control parameters.

FIG. 8 shows PC5 interface for ProSe direct discovery. Referring to FIG.8, UE A and UE B perform ProSe direct discovery using ProSe protocol viaPC5-D. Radio protocol stack (AS) for ProSe direct discovery consists ofonly MAC and PHY. The AS layer performs function of interfaces withupper layer (ProSe Protocol). The MAC layer receives the discoverymessage from the upper layer (ProSe Protocol). The IP layer is not usedfor transmitting the discovery message. The AS layer also performsfunction of scheduling. The MAC layer determines the radio resource tobe used for announcing the discovery message received from upper layer.The AS layer also performs function of discovery PDU generation. The MAClayer builds the MAC PDU carrying the discovery message and sends theMAC PDU to the physical layer for transmission in the determined radioresource. No MAC header is added.

There are two types of resource allocation for discovery messageannouncement, which include Type 1 (UE autonomous resource selection)and Type 2 (scheduled resource allocation). Type 1 is a resourceallocation procedure where resources for announcing of discovery messageare allocated on a non UE specific basis. In Type 1, the eNB providesthe UE(s) with the resource pool configuration used for announcing ofdiscovery message. The configuration may be signaled in broadcast ordedicated signaling. The UE autonomously selects radio resource(s) fromthe indicated resource pool and announce discovery message. The UE canannounce discovery message on a randomly selected discovery resourceduring each discovery period. Type 2 is a resource allocation procedurewhere resources for announcing of discovery message are allocated on perUE specific basis. In Type 2, the UE in RRC_CONNECTED may requestresource(s) for announcing of discovery message from the eNB via RRC.The eNB assigns resource(s) via RRC. The resources are allocated withinthe resource pool that is configured in UEs for monitoring.

For UEs in RRC_IDLE, the eNB may provide a resource pool for Type 1based discovery message announcement in SIB 19. UEs that are authorizedfor Prose direct discovery use these resources for announcing discoverymessage in RRC_IDLE. Alternatively, the eNB may indicate in SIB 19 thatit supports ProSe direct discovery but does not provide resources fordiscovery message announcement. UEs need to enter RRC_CONNECTED in orderto request resources for discovery message announcement.

For UEs in RRC_CONNECTED, a UE authorized to perform ProSe directdiscovery announcement indicates to the eNB that it wants to performProSe direct discovery announcement. The eNB validates whether the UE isauthorized for ProSe direct discovery announcement using the UE contextreceived from MME. The eNB may configure the UE with resource pool forType 1 for discovery message announcement via dedicated signaling. TheeNB may configure resource pool along with dedicated resource in theform of time and frequency indices for discovery message announcementvia dedicated RRC signaling. The dedicated resources allocated by theeNB are valid until the eNB re-configures the resource(s) by RRCsignaling, or the UE enters RRC_IDLE.

Authorized receiving UEs in RRC_IDLE and RRC_CONNECTED monitor resourcepools used for Type 1 and resource pools for Type 2. The eNB providesthe resource pool configuration used for discovery message monitoring inSIB 19. The SIB 19 may contain detailed ProSe direct discoveryconfiguration used for announcing in neighbor cells of intra-frequencyas well.

Synchronous and asynchronous deployments are supported. Discoveryresources can be overlapping or non-overlapping across cells.

A UE, if authorized by the network, can announce discovery message onlyon serving cell. The UE can monitor discovery resources in the same aswell as other frequencies than the serving cell, in same or differentPLMNs. The serving cell may provide in SIB 19 a list of frequenciesalong with PLMN ID on which the UE may aim to monitor discovery message.The serving cell does not provide detailed ProSe discovery configurationfor other carrier frequencies. The UE shall read SIB 19 and otherrelevant SIBs on other carriers if it wants to perform discovery messagemonitoring on those carriers. Obtaining ProSe direct discoveryconfiguration by reading SIB 19 (and other SIBs) of an inter-frequencyand/or inter-PLMN cell shall not affect the UE's Uu reception on theserving cell(s). The UE performs intra-frequency ProSe direct discoveryannouncement in subframes in which a ProSe direct discovery resourcepool is configured and the UE is not expected to perform uplink Uutransmission. In this case, the UE shall not create autonomous gaps.Intra-frequency, inter-frequency and inter-PLMN ProSe direct discoverymonitoring shall not affect Uu reception. The UE uses DRX occasions inRRC_IDLE and RRC_CONNECTED or second RX chain if it is available, forintra-frequency, inter-frequency and inter-PLMN discovery messagemonitoring. The UE shall not create autonomous gaps. An RRC_CONNECTED UEsends ProSe UE Information indication to the serving cell if it isinterested or no longer interested in intra-frequency, inter-frequencyor inter-PLMN discovery message monitoring.

FIG. 9 shows an example of UE-to-Network Relay and UE-to-UE Relay.Referring to FIG. 9, UE1 performs as a ProSe UE-to-Network Relay UE(hereinafter, relay UE). Relay UE is a UE that provides functionality tosupport connectivity to unicast services for remote UE(s). UE2 performsas a remote UE. Remote UE is a ProSe-enabled public safety UE thatcommunicates with a PDN via a ProSe UE-to-Network Relay. That is, UE1,i.e. relay UE, receives from control signal/data from UE2, i.e. remoteUE, which is required to be relayed to the network or another UE, i.e.UE3. If the control signal/data is relayed to the network, it mayconsist of UE-to-Network Relay. If the control signal/data is relayed toUE3, it may consist of UE-to-UE Relay.

In order to support the relay functionality for ProSe, additionalsignaling may be required to be supported between core network entitiesand within radio access network for authorizing the relay UE and otherfunctionalities. Some networks may support relaying functionality in itscell, while others may not support relaying functionality. From theperspective of the relay UE, it is desirable to be camped on the cellwhich supports relaying functionality.

In order to solve the problem described above, a method for transmittinga relay support indication according to an embodiment of the presentinvention is described below. According to an embodiment of the presentinvention, upon receiving the relay support indication from a network,the UE may perform cell selection or cell reselection. In thedescription below, UE-to-Network Relay may be focused for theconvenience, however, the present invention is not limited to thereto.The present invention described below may be applied to UE-to-UE Relayas well. Relay may refer to UE-to-UE relay as well as UE-to-NetworkRelay in the description below. Further, it is assumed that UE1(receiver UE) is relay UE that can provide the relay service and UE2(transmitter UE) is a remote UE that wants to get the relay service.Further, there may be two types of relay services, one of which is arelay service for 1:M data transmitted by remote UE and the other is arelay service for 1:1 data transmitted by remote UE.

FIG. 10 shows a method for transmitting a relay support indicationaccording to an embodiment of the present invention.

In step S100, the UE, which can be a relay UE to be camped on a cellsupporting relay functionality, receives information on whether a cellsupports a relay functionality or not. The information may be broadcastby the cell. The relay functionality may be used only for ProSe (i.e.UE-to-Network Relay or UE-to-UE Relay). The information may furtherinclude a white-list which is a list of cell identities/frequencies inwhich the relay functionality is supported. Alternatively, theinformation may further include a black-list which is a list of cellidentities/frequencies in which the relay functionality is notsupported. Alternatively, the information may further includeconfiguration information related to the relay functionality.

In step S110, upon receiving the information, the UE performs a cellselection or cell reselection according to the received information. TheUE may consider the corresponding cell/frequency as barred for relayfunctionality in the following cases.

-   -   If the information described above is absent in broadcast        information in the cell; or    -   If the information descried above indicates that the current        cell does not support relay functionality; or    -   If a cell identity of the current serving cell or frequency        corresponding to the current serving cell is not included in the        white-list; or    -   If a cell identity of the current serving cell or frequency        corresponding to the current serving cell is included in the        black-list.    -   If configuration information related to the relay functionality        is not included in broadcast information in the cell or relevant        system information is not scheduled.

When the cell is considered as barred for relay functionality, i.e. itis indicated that the cell does not support relay functionality or thecell is treated as if barred, the UE may not be permitted toselect/reselect the cell, not even for emergency calls. Further, the UEmay select/reselect another cell, since the current cell is consideredas barred. If the cell is a closed subscriber group (CSG) cell, the UEmay select another cell on the same frequency if theselection/reselection criteria are fulfilled. Else, if the fieldintraFreqReselection in field cellAccessRelatedInfo inSystemInformationBlockType1 message is set to “allowed”, the UE mayselect another cell on the same frequency if reselection criteria arefulfilled. In this case, the UE may exclude the barred cell as acandidate for cell selection/reselection for 300 seconds. Alternatively,if the field intraFreqReselection in field cellAccessRelatedInfo inSystemInformationBlockType1 message is set to “not allowed”, the UE maynot reselect a cell on the same frequency as the barred cell. In thiscase, the UE may exclude the barred cell and the cells on the samefrequency as a candidate for cell selection/reselection for 300 seconds.

Meanwhile, while the UE is camped on a suitable cell which support relayfunctionality, the UE may always consider the current frequency of theserving cell to be the highest priority frequency (i.e. higher than theeight network configured values), irrespective of any other priorityvalue allocated to this frequency. Further, if the UE capable of relayfunctionality is configured to perform relay while camping on afrequency, the UE may consider that frequency to be the highestpriority. The UE may consider the current frequency to be the highestpriority during performing relaying functionality. If the UE detects oneor more suitable cells on different frequencies which support relayfunctionality, then the UE may reselect one of the detected cellsirrespective of the frequency priority of the cell the UE is currentlycamped on, if the corresponding detected cell is the highest ranked cellon that frequency.

Further, the UE capable of relay functionality may currently beperforming as relay UE in RRC idle mode, or the UE capable of relayfunctionality, which is expected to be performing as relay UE (i.e.currently not performing as relay UE), may stay in RRC idle mode. If theUE does not find a suitable cell which support relay functionalitywithin a threshold time, the UE capable of relay functionality may becamped on a suitable cell regardless of the above invention.

FIG. 11 shows a wireless communication system to implement an embodimentof the present invention.

An eNB 800 includes a processor 810, a memory 820 and a transceiver 830.The processor 810 may be configured to implement proposed functions,procedures and/or methods described in this description. Layers of theradio interface protocol may be implemented in the processor 810. Thememory 820 is operatively coupled with the processor 810 and stores avariety of information to operate the processor 810. The transceiver 830is operatively coupled with the processor 810, and transmits and/orreceives a radio signal. The transceiver 830 may transmit information onwhether a cell supports relay functionality or not.

A UE 900 includes a processor 910, a memory 920 and a transceiver 930.The processor 910 may be configured to implement proposed functions,procedures and/or methods described in this description. The processor910 may perform a cell selection or cell reselection according to theinformation received from eNB 800. Layers of the radio interfaceprotocol may be implemented in the processor 910. The memory 920 isoperatively coupled with the processor 910 and stores a variety ofinformation to operate the processor 910. The transceiver 930 isoperatively coupled with the processor 910, and transmits and/orreceives a radio signal.

The processors 810, 910 may include application-specific integratedcircuit (ASIC), other chipset, logic circuit and/or data processingdevice. The memories 820, 920 may include read-only memory (ROM), randomaccess memory (RAM), flash memory, memory card, storage medium and/orother storage device. The transceivers 830, 930 may include basebandcircuitry to process radio frequency signals. When the embodiments areimplemented in software, the techniques described herein can beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The modules can be stored inmemories 820, 920 and executed by processors 810, 910. The memories 820,920 can be implemented within the processors 810, 910 or external to theprocessors 810, 910 in which case those can be communicatively coupledto the processors 810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

The invention claimed is:
 1. A method for performing, by a userequipment (UE), a cell selection or a cell reselection in a wirelesscommunication system, the method comprising: receiving information thatindicates whether a relay functionality is supported by a cell, whereinthe relay functionality is restricted to use only for proximity-basedservices (ProSe); and performing a cell selection or a cell reselectionaccording to the received information, wherein, when the UE isconfigured to perform the relay functionality while camping on a currentfrequency, the UE considers the current frequency to be a highestpriority when the relay functionality is performed, wherein the relayfunctionality contains two types of relay services including a firstrelay service for 1:M data transmitted by a remote UE and a second relayservice for 1:1 data transmitted by the remote UE, and wherein the relayfunctionality is performed while the UE is in a Radio Resource Control(RRC) idle mode.
 2. The method of claim 1, wherein the information isbroadcast by the cell.
 3. The method of claim 1, wherein the informationincludes a white-list which is a list of cell identities or frequenciesin which the relay functionality is supported.
 4. The method of claim 1,wherein the information includes a black-list which is a list of cellidentities or frequencies in which the relay functionality is notsupported.
 5. The method of claim 1, wherein the information indicatesthat the cell does not support the relay functionality.
 6. The method ofclaim 5, wherein the cell selection or the cell reselection is performedtowards another cell on the same frequency as the cell if the cell is aclosed subscriber group (CSG) cell.
 7. The method of claim 5, whereinthe cell selection or the cell reselection is performed towards anothercell on the same frequency as the cell if intraFreqReselection in fieldcellAccessRelatedlnfo in SystemInformationBlockType1 message is set to“allowed”.
 8. A user equipment (UE) in a wireless communication system,the UE comprising: a memory; a transceiver; and a processor coupled tothe memory and the transceiver, wherein the processor is configured to:control the transceiver to receive information that indicates whether arelay functionality is supported by a cell, wherein the relayfunctionality is restricted to use only for proximity-based services(ProSe); and perform a cell selection or a cell reselection according tothe received information, wherein, when the UE is configured to performthe relay functionality while camping on a current frequency, the UEconsiders the current frequency to be a highest priority when the relayfunctionality is performed, wherein the relay functionality contains twotypes of relay services including a first relay service for 1:M datatransmitted by a remote UE and a second relay service for 1:1 datatransmitted by the remote UE, and wherein the relay functionality isperformed while the UE is in a Radio Resource Control (RRC) idle mode.9. The UE of claim 8, wherein the information is broadcast by the cell.10. The UE of claim 8, wherein the information includes a white-listwhich is a list of cell identities or frequencies in which the relayfunctionality is supported.
 11. The UE of claim 8, wherein theinformation includes a black-list which is a list of cell identities orfrequencies in which the relay functionality is not supported.